Electrical heater



April 25, 1933- c. H. CHAPMAN 1,905,801

ELECTRICAL HEATER Filed March 18, 1930 Inventor: Charles H Chapman by MW His Attorneg.

Patented Apr. 25, 1933 UNITED STATES PATENT OFFICE CHARLES E. CHAPMAN, OF SC'QTIA, NEW YORK, LESIGIN'OR '10 GENERAL COMPANY, A CORPORATION OF NEW YORK ELECTRIC ELECTRICAL HEATER Application filed March 18,

"ment overload protection for electric motors of difierent ratings. To facilitate interchange of the heaters,'they must be removably mounted. To obtain the maximum heatin eificiency, the heater must be arrange "to substantially surround the bimetallic element.

50 present invention. 7 i

For the larger current carrying capacities, difiiculties may be experienced due to burnout of the heaters under excessive overload conditions such as short circuits or the like unless special provision is made for increasing the overload capacity of the heater. Furthermore, with the very large current capacity heaters, it is difiicult, due to the large cross section required for the heater element to form the element so as to surround the bimetallic element.

The principal object of the present invention is to provide an improved form of large current capacity electrical heaters for the thermal relays which maybe mounted for ready removability and whichdistributes heat to. all sides of the bimetallic element and at the same time is provided withincreased thermal capacity so as successfully to, with-' stand excessive overload current.

In the accompanying drawing Fifiwldfi a perspective view showing a bimeta ie type of thermal relay provided with the improved form of .removably mounted large current capacity electrical heater with the parts of therelay in disassembled relation; Fig. 2' is a sectional view of the thermal relay with the electrical heater in operative osition surrounding thethermal element an Fig. 3' is a perspective view of a modified form of electrical heater. for the relay embodying the v removablyl t rremovably mounted large current capac ity.-fto

1930. Serial 1W0. 486,815.

In Fig. 1 the thermal relay is shown as used in connection with the electromagnetically operated switch 10 which is mounted on the base 11 from which the terminal supports 12 and 13 extend for mounting the thermal relay thereon. The thermal relay comprises the substantially L shaped channel frame 14 upon which the bimetallic thermal element 15 is fixed at one end with the other end 15 extending into abutting engagement with the movable member 16 which is rotatably mounted by the pin 17 on the frame 14. The spring 18 serves to bias the movable member 16 into abutting engagement with the free end 15 of the thermal element. When the thermal element 15 flexes to release the movable member 16, the latter engages with the bar 19 which is pivotally mounted on the pin 20 and is arranged to actuate the contact 21 out of engagement with the stationary contact 22.

The large current capacity electric heater 25 is provided for heating the thermal element 15 to cause flexure thereof. In accordance with the present invention the electric. heater 25 is formed with a main heat generating portion 26 from the edge of which the heat conducting tongue 27 extends so as to increase the overload, capacity of the heater. The main heat generating portion of the heater as shown is in the form of a substantially flat bar 26 provided with the holes 28 and 29 at the'opposite ends thereof for mounting and electrically con-v necting t e heater to the supporting terminals 12 and 13 by means of. the screws 30 and 31.

' With this construction the heat conduct- 26'of the heater therefrom. Thetongue 27 v as shown extends fromthe left hand edge of the bar'26 and is looped around so asto bring the end thereof almost into engagement, with the right hand side of the bar 26. In h's way a'space between the bar-26 and the Ages isprovided f or receiving the bimetallic element\15 therebetween as shown v more clearly inthe sectional view of Fig. 2.

lhus the heater substantially surrounds the bimetallic element except for the extreme end portions of the element and serves to dis- A triblite the heat generated in the bar portion 26 of the heater to both the front and rear sides of the thermal element. 4

With the tongue 27 extending from the middle portion of the heater, it will be evident that this portion is of materially larger cross section than the more restricted end portions of the heater element on either side thereof. Thus the increased thermal capacity of the middle portion of the thermal element insures against burnout which ordinarily occurs with the usual form of electrical heaters.

To assemble the parts of the thermal relay into operative relation, the movable member 16 is swung about the pivot 17 away from the free end 15 of the thermal element. The

looped tongue 27 of the heater is then slipped over the free end of the thermal element and the bolt passed through the opening 28 in the heater and the corresponding opening formed in the upstanding lug 32 extending from the frame 1 The bolt 30 is then screwed into the threaded opening provided in the terminal support 12. The channel sides of the frame 14 engage with the support 12 so as to hold the frame securely in position with the movable element 16 located in operating relation with the bar 19. Upon passing the bolt 31 through the opening 29 in the lower end of the heater and tightening the bolt in the threaded opening provided in the terminal support 13, the lower endof the heater is mechanially and electrically connected with the support. Toplace the relay in operative condition, it is now only necessary to release the tripping member 16 to permit the same to turn about the pin 17 in accordance with its bias so asto engage with the free end 15 of the thermal element 15 as'shown in Fig. 1.

With the terminal supports 12 and 13 connected in the circuit control by the switchylO, the passage of the current therebetween is restricted principally to the bar portion 26 of the heater. The heat generated in the bar portion 26, however, is conducted by the looped tongue 27 and radiated to the rear side of the thermal element 15. The bar portion 26 of the heater radiates heat directly to the front side of the thermal element 15.

In case of an excessive overload current, the increased heat storage capacity provided by the tongue 27 insures against burnout of the heater during the short time interval required for flexure of the thermal element 15 to release the member 16 and open contacts 21 and 22 and thereby eilect operation or" the electromagnetic switch 10 to interrupt the circuit, With overload currents of normal value, the increased heating efiiciency ob.- tained by the conduction of heat through the tongue 27 insures response of the thermal element 15 with the desired time delay action.

In case a more equalized conduction of the heat from the bar portion 26 of the thermal element and a more uniform distribution of the heat to the thermal element 15 is desired, the modified heater construction shown in Fig. 3 may be employed. In this construction a plurality of tongues 27 are provided extending in staggered relation from the opposite edges of the main heat generating bar portion 26 of the heater element. Each of the tongues 27 may be looped around in substantially the same manner as the tongue 27 shown in Fig. 1 so as to enclose the thermal element 15 between the tongue and the bar section of the heater. This modified construction also more effectively restricts the path of the current through the heater to the main heat generating portion 26.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. An electric heater for a bimetallic strip comprising a fiat portion extending the length of the heater for conducting the heating current and provided with terminal engaging apertures, a portion intermediate the ends of said fiat portion and extending from a side thereof and cooperating with said flat portion to provide a substantially closed loop for surrounding a bimetallic element for rediating heat thereto to all sides thereof, said looped portion having a substantial heat storage capacity. c

2. An electric heater for a bimetallic strip comprising a main portion having a flat bar shape for engagement'with a pair of terminals, a portion extending from the side of said main portion and cooperating with said main portion to form asubstantially closed loop for surrounding a bimetallic strip for radiating heat thereto toall sides thereof, said extending portion having a relatively high heat storage capacity to prevent burning out of said heater on momentarily large currents.

3. An electric heater for a bimetallic strip comprising a flat portion for conducting the heating current and provided with terminal engaging apertures at the ends of said flat portion, a heat conducting tongue extending from a side of said flat portion out of the path of the heating current and forming a substantially closed loop with said fiat portion, said heater being adapted to receive a bimetallic element within said loop whereby said bimetallic element will receive radiated heat to all sides thereof from said loop.

a. An electric heater for a bimetallic element comprising a resistance member having a heat-generating portion adapted to engage terminal at its ends, il-shaped portion of substantial heat-storage capacity extending :rom one side of and intermediate the ends of said heatenerating portion and forming a substantiafiy closed loop with said heatgenerating portion, said heater being adapted to recelve a bimetallic element within said loop whereby said bimetallic element will receive radiated heat from all sides thereof.

5. An electric heater for a bimetallic strip comprisin a resistance member having a fiat portlon a a ted to engage terminals at the ends thereoi: a. heat conducting portion of substantial heat storage capacity extending from said flat portion intermediate the ends of said flat ortion and forming a substantially closed loop with said fiat portion whereby a bimetallic element laced within said loop will have heat ra iated thereto from all sides thereof.

6. An electric heater for a bimetallic strip comprising a substantiall flat bar of resistance material provided with terminal engaging apertures and having a heat conducting tongue of substantial heat storage capacity extendin from the edge thereof and looped in s ac relatiomwith thebar and forming 5 a su stantially closed loop with said bar for surrounding a bimetallic strip, whereb said bimetallic stri will receive radiate heat thereto from all sides thereof.

In witness whereof, I have hereunto set my hand this 17th day of March 1930.

CHARLES H. CHAPMAN. 

